Hey everybody, Im Mark, and I have been working on this 1991 Jaguar Sovereign 4.0 for awhile now and i cant seem to get it running right...since august... lately i found out that it wont even start up unless i disconnect the coolant temperature sensor (very weird) I've replaced everything that might be causing it to stall, and when i do get it running i have to keep my foot on the pedal and then it starts popping through the intake, if i let go of the pedal, it stalls.... please help!

Everything here i replaced and checked...

New Fuel lines
New Fuel pump
New Fuel regulator
New Fuel filter
New Mass air flow sensor
New intake manifold gasket
New idle air control valve -(programmed)
New plugs & wires
Checked catalytic converter
Checked distributer
Cleaned throttle body
Cleaned injectors
replaced computer ECU

what can be causing it to do this?

 

never had this on a Jag but I had an old suzuki that had a similar problem and the distributor was on upside down so it was running 180* off. I felt stupid but what do you do.

Just a thought.

 

Marco,

First thought is the TPS (Throttle Position Sensor) located under the throttle body. It needs to be set and calibrated.....did you do that???

It is responsible for sending a signal to the ECU for fuel/air mixture.

You'll need your meter to monitor the adjustment. See the attachment.

Good luck

 

Mark:
Is the VCM giving you no codes?

Scott

 

ill give these all a try, thanks guys, ill report back soon

 

midwestjag: no codes where shown

 

Rob:
what do i need to go about setting the TPS?

ps thanks for the pdf link.

 

Marco,

This is a great thread to read for handling the TPS setting. Be sure to scroll down to a contribution made by "gunnerman" about half was down the page, and the contributions after his.

Link to page:

https://www.jaguarforums.com/forum/xj40-25/tps-66979/

You need a voltmeter to check the settings.

If the voltage readings are out of range, you will simply move the TPS body slightly, tighten it down and go through the readings again. You can see in the pdf I gave you earlier, the TPS body has slots for the set screws in order to adjust the body to & fro from it's position.

 

hey everyone just a quick note,
another thing i noticed as i was checking the TPS voltage (which turned out reading at 4.85 volts) i had everything off... the maf, intake, filter, etc. i thought to myself, what would happen if i started it up with out the Mass air flow sensor on, being me, i went and started it up, and it ran and idled great! i even took it around the block, i had to work the gas a bit to get it up the hill, but it ran better than ever! do you think it could be the MAF? wth!

 

Marco,

Could be the MAF, but in your original post you indicated you replaced it with a new unit.....so did you try the old MAF?

 

Rob:

yes a did replace the old one with a second hand one, but it seems that both aren't working properly, is there a special way to set up the MAF? do i just plug it in and go?

 

Marco,

As far as I know there is nothing you can do to the MAF other than ensure the contact points are clean on the unit and it's connection point.

Maybe someone can chime in on this thread and enlighten us if there is an adjustment on it.

I've never had a problem with mine. Are you certain the used one sold to you is proper for your vehicle? There are varieties dependent on the VIN and if you bought it on ebay...... well they tell you anything to sell the components.

See this link and expand on item #19 and compare the unit model number you have with the information:

Air Flow Meter Air Box - Parts For XJ6 (2.9, 3.2, 3.6, 4.0) from (V)500001 to (V)667828 | Jaguar Classic Parts UK

Let us know

 

UPDATE:

i checked the VCM again with everything connect (tps, maf) got a FUEL FAIL 14 code...

 

Coolant temp sensor faulty - not expensive, can cause all manner of running problems - when mine was fried, got hestitation, stalling, and generally crap running. Simple fix, 10 minute job - Good luck!

 

Good Deal!!!

VCM finally came through, very helpful.

I've never had a problem with my coolant sensor (surprisingly) so I have no idea on time involved, but our friend Lawrence apparently has and he is a trusted source.

Good luck

 

Ahh cool, im gonna get that part and install asap, fingers crossed! Thanks guys

 

update

 

alight guys so...

ok while i was waiting for the CTS to arrive i thought id figure out what was draining the battery, it was the aftermarket radio i put it that was causing it, so i finally fixed the drain after 6 months of recharging, now my battery is holding a charge! i thought i give the engine a crank and it sounded like the engine was missing... the next day the coolant temp sensor came in, installed it, tried to start it up but now it wouldn't start at all, no codes but as i was cranking the engine, the VCM just read just FAIL...weird..., now it wont even budge, %$#%@!!!!!:icon_e vil:

i did some research and.... could it be the crank position sensor? could it have been going? should i grab a new one?????

 

Marco:
in a word, yes. I think the number one cause of non-start for the XJ40 is the Crankshaft sensor. So, hopefully a new one will do the trick. Otherwise... Back to the drawing board.
Scott

 

Marco,

When you state the reading was 4.85 volts, are you referencing the "throttle wide open" reading is at 4.85v and the idle position reading was......? According to that tech doc the idle reading should be around ..60v.

Frankly, I'm a little gun shy to give advice (CPS) at this point , hate it when you advise and things don't go right....

let us know.